References are made of U.S. Pat. No. 6,190,382, issued on Feb. 20, 2001, and U.S. patent application Ser. No. 10/306,757, filed with the United States Patent and Trademark Office on Nov. 27, 2002 and entitled: “Radio-Frequency-based Catheter System with Improved Deflection and Steering Mechanisms,” which include the same inventors as the present application and are incorporated hereto in full by reference.
Cardiac arrhythmias are a major cause of morbidity and mortality in humans, especially atrial fibrillation. Atrial fibrillation may affect up to 10% of the population by the 7th or 8th decade of life, and is responsible for tens of thousands of hospitalizations each year at a cost of over a billion dollars. Extensive research in the past decade has shown that atrial fibrillation is due to electrical reentry phenomenon in the atria, causing a rapid depolarization of the tissue at rates of 350-500 beats per minute. The rapid electrical depolarization causes inadequate contraction, which can lead to stasis of blood with clot formation that can cause a stroke, the single most debilitating and life threatening complication of atrial fibrillation. The risk of stroke can be reduced by anticoagulation, but is not eliminated. In addition, the rapid ventricular response caused by atrial fibrillation can lead to congestive heart failure, another significant cause of morbidity and mortality in patients with atrial fibrillation. Finally, atrial fibrillation causes debilitating symptoms in a majority of patients. Atrial fibrillation can be controlled with antiarrhythmic medications, but only about 50% of patients respond. Another option for treatment is pacemaker implantation, with or without ablation of the AV node for rate control, but this does not reduce the risk of stroke, nor relieve symptoms in all patients. Consequently, since current therapies are inadequate to prevent recurrence of atrial fibrillation in a majority of patient, alternative approaches to curing atrial fibrillation have been sought.
Atrial fibrillation, in its paroxysmal stage, has been shown to be triggered by focal premature electrical depolarizations in the pulmonary veins, which can be cured by electrical isolation of the pulmonary veins from the left atrium using limited map-guided radio-frequency catheter ablation. However, this approach is only effective in approximately 70-80% of patients with paroxysmal atrial fibrillation, and in fewer than 20% of patients with chronic or persistent atrial fibrillation. In addition, ablation in or around the pulmonary veins may cause their stenosis in a small percentage of cases, a serious and potentially life-threatening complication.
A more extensive ablation procedure is required in patients with persistent atrial fibrillation, which is to interrupt all potential reentrant electrical circuits in the atria. One such procedure is commonly known as the MAZE operation. Maze operation is applied to block potential reentrant electrical activation in the right and left atria, while allowing conduction from the sinus node to the AV node through a maze-like pathway and normal AV conduction and AV synchrony to persist following cure of atrial fibrillation. However, this procedure must be done as an open-heart surgery, typically while the patient is on cardiopulmonary bypass. This type of surgery is associated with significant potential morbidity and a mortality rate of 2-5%. Therefore, since most patients are reluctant to undergo such an invasive procedure, and their overall medical condition may prohibit them from taking the risks associated with such a procedure, a less invasive approach is desirable.
Various radio-frequency catheter ablation techniques have been applied for curing many atrial arrhythmias. These include supraventricular tachycardia, atrial flutter and more recently focal triggered paroxysmal atrial fibrillation. These techniques have also been attempted for treatment of persistent atrial fibrillation. Multiple focal lesions can be placed to form linear ablation lesions surrounding the pulmonary veins in the left atrium with a line anchoring this set of lesions to the mitral valve annulus, alone or in combination with a set of linear lesions in the posterior and septal right atrium and sub-Eustachian isthmus (i.e., so called flutter line). Linear ablation using such techniques has been shown to be effective in up to 70% of patients in some studies, but continued treatment with antiarrhythmic medications is often required. In addition, the occurrence of incomplete lines of ablation effected by multiple focal lesions is common, resulting in a high risk of recurrent reentrant atrial tachycardia thus, requiring further ablation. Furthermore, because of the prolonged procedure time required to complete the ablation using this multiple focal lesions approach, there is up to a 5% risk of embolic stroke and other serious complications.
As referenced in U.S. Pat. No. 6,190,382 and U.S. patent application Ser. No. 10/306,757, effective treatments for atrial fibrillation with catheter ablation requires the creation of long or overlapping lineal or curvilinear ablation lesions on the inner surface of the atrium. These lesions can then act as barriers to the conduction of electrical impulses, thus preventing atrial fibrillation.
U.S. Pat. No. 6,190,382 and U.S. patent application Ser. No. 10/306,757, disclose a radio-frequency or microwave-energy based catheter for ablating biological tissues within the body vessel of a patient. The catheter has a proximal portion, a distal portion with a distal end and a lumen extending from the proximal portion to the distal portion. The catheter incorporates an elongated catheter guide that is located within the catheter lumen and is secured to the distal portion of the catheter at one end, with the other end portion extending proximally within the catheter lumen to be coupled to a positioning mechanism. A significant advantage of the catheter guide is that it is deployable beyond the distal end of the catheter to form a loop, which is conformable to the interior contour of the body vessel. The catheter guide carries the catheter with a radio-frequency or microwave energy based antenna incorporated at the distal portion of the catheter. The antenna includes a helical coil, which accommodates the catheter guide passing through it. The radio-frequency antenna is adapted to receive and irradiate radio-frequency energy in the microwave range at a frequency typically greater than 300 Megahertz (MHz) in the electromagnetic spectrum for ablating biological tissue along a biological ablation pathway.